We propose to extend our work on the degradation of tyrosine, and related compounds, by the eukaryotic microorganism, Trichosporon cutaneum. A novel pathway has already been outlined: it involves deamination to give 4-hydroxycinnamic acid, loss of the side-chain and formation of protocatechuic acid, and ring-fission of hydroxyquinol. Loss of the side chain by hydration and aldol fission has been described by other authors for other organisms: but synthetic beta-(4-hydroxyphenyl)-hydracrylic acid has never been used in previous studies, and consequently its ATP, CoA-dependent aldol fission (which our work suggests) has not yet been studied. This organism also appears to metabolize 3-hydroxyphenylacetic acid by one hydroxylation prior to ring-fission, and 4-hydroxyphenylacetic acid by two. Interesting problems of enzyme derepression are involved in these sequences, and they are under investigation. In another area, the enzymatic removal by various microorganisms of methoxyl groups from naturally-occurring, and chemically synthesized, compounds is under investigation. Three different demethylation systems can operate according to the chemical structure of the compound subject to degradation: monooxygenase attack upon the methyl group; release of methanol by hydrolysis after preliminary reactions have given rise to an ester grouping; or explusion of methanol during hydration of a suitably positioned ethylenic linkage.